I do and have my athletes do so, I refer to them as OWS Even for those who can't do OWS often I have them do steady long swims simulations every now and then (i.e. 4x1000 short rest). The guy I helped for the 10K would do a weekly 3-6mi OWS on a 1/2 mile length pond during the specific phase
Also, I disagree somewhat with the reasoning about not swimming if your technique breaks down; IMO you must learn to swim specially when tired. As your fitness improves, your 'form' will break down less. That's one of the reasons I have athletes do drills but also, swim more (short, easy, long, fast, tempo, OWS, etc.).
As for only swimming 2x week, that might be challenging to get you ready, you might need 8-10k+ sessions.
I figured a 2x/week swim might be an issue. I've always "gotten by" on this for all of my IMs, but I do realize 10K swim is another level. I will give 3x swims serious consideration. I know everyone tries to make a balance with the 3 disciplines (and life) and I've always chosen to give swimming the short end of my training since I know it will only be about 10% of a race. Maybe I should reframe my 10K swimming goal and say that I'm not so much training to "race" the 10K, but to get through it well enough to get to the bike and run in reasonable shape. I know that to the the more dedicated swimmers (and to the coaches) out there that 2x and even 3x is not optimal and I understand that, but that's the tradeoff I'm considering since I also have to train for a 90+170mi bike and a double mary.
Is doing a 4x1000 for training better than just swimming a straight 4000? How often are you recommending OWS/steady long swim simulations?